Kent Home Cinema

Some of the larger subwoofers we sell; SVS PB13 Plus, Velodyne DD18 and MJ Acoustics Ref 1 MkIII kick out some serious bass and can be safely driven to very loud decibel levels in most rooms.  This prompted me to research what decibel levels are safe, what causes these noises in the domestic home.  Luckily the National Institute for Occupational Safety & Health (NIOSH) has compiled a list of the decibel measurements (dBA) for common noises you might be exposed to each day at home, work or during recreational activities.  A decibel is a unit that expresses intensity or power.  So to see what your exposure is to unsafe noises with some of the following examples:

Home: 

• 50 dBA – Refrigerator
• 50-80 dBA – Electric shaver
• 50-80 dBA – Electric shaver
• 60-95 dBA – Hair dryer
• 75-85 dBA – Flushed toilet
• 80 dBA – Ringing phone, Vacuum cleaner
• 110 dBA – Crying baby
• 135 dBA – Noisy squeeze toys

Work:

• 40 dBA – Quiet office/ library
• 65-95 dBA – Power lawnmower
• 90-115 dBA – Subway
• 105 dBA – Snow blower
• 120 dBA – Ambulance
• 140 dBA – Airplane take-off
• 180 dBA – Rocket launching from pad

Recreation:

• 70 dBA – Freeway traffic
• 90 dBA – Large restaurant
• 95-110 dBA – Motorcycle
• 100 dBA Personal stereo
• 110 dBA – Car horn
• 115 dBA – Night Club
• 117 dBA – Football game (stadium)
• 140 dBA – Gunshot
• 150 dBA – Firecracker
• 157 dBA – Balloon pop
• 170 dBA – Shotgun

Other:

• 0 dBA – Softest level the human can hear
• 10 dBA – Normal breathing
• 30 dBA – Whisper
• 60 dBA – Normal conversation
• 80 dBA – Shouting
• 105 – 120 dBA – Thunder
• 110 dBA– Shout in the ear, Climax to film Armageddon!!

And just for the record!

• 116-119 dBA – From 2 x SVS PB13 Ultra Subwoofers at Dolby Reference Level

But how much is too much?   

NIOSH states that the maximum amount of time a person can be exposed to 85 dBA without experiencing hearing damage is 8 hours; this is the average level of noise a person hears every day. However, continuous exposure to 85 dBA beyond the 8-hour limit will cause hearing loss. If a person is exposed to level above 85 dBA, the risk of hearing loss increases in a shorter amount of time. The maximum time allowed for 110 dBA (e.g. a crying baby) is 1 minute 29 seconds. If a person is exposed to a noise that has a measurement of 140 dBA (e.g. airplane departure), immediate inner ear damage would result.

Hope this proved insightful and useful.

Hopefully this is a simple explanation on why subwoofers exist and what part they play in a surround sound system.

A Subwoofer or “Sub” is a speaker specifically designed to reproduce the sounds at the lowest end of the audible frequency range, otherwise known as Bass. This is also referred to as “LFE” (Low Frequency Effects) and is essentially about moving low frequencies through the air.  Low frequencies are long wavelengths that take a greater amount of power to produce than the mid-range or high frequency sounds which are made up of shorter wavelengths.

LFE can provide added drama to a film with dynamic special effects e.g. bombs exploding, buildings collapsing or even a thunder storm.  The subwoofer in a home cinema set up is therefore aimed at producing these deep bass elements in a film soundtrack.   A subwoofer can also reach depths of sound on music that a standard “full range” speaker cannot achieve.  When you see 5.1, 6.1 or 7.1 (or even nowadays 7.2) the .1 or .2 advertised on a surround system, AV receiver or DVD / Blu-ray player, signifies that the LFE has its own dedicated channel.

Types of Subwoofer

Passive Subwoofers.  These subwoofers are powered by an external amplifier, like the rest of the speakers in the surround sound system. As low bass needs more power to reproduce low frequency sounds, the Amplifier or AV Receiver has to provide enough output power to sustain the bass effects in the subwoofer without draining the amp and having a detrimental effect on the performance of the other speakers in the system.   Room size, speaker demand and your personal taste for bass all has to be taken into account.

Powered or Active Subwoofers.  Most subwoofers on sale now are powered (amplified or active) models.  Essentially they have a built in amplifier to ensure there is adequate power provided when needed.  Also freeing up spare” power to drive the mid-range and tweeters in your surround system more easily.  The subwoofer driver characteristics are also matched by the manufacturer for optimum performance.  Connection is also made simpler as only one cable is required (Line Out/In) specifically for the LFE Bass channel. 

Presenting the bass

Once the power issue has been resolved, manufacturers also go about presenting the bass via different design methods.  These include down firing or front firing driver configurations, that can have sealed, ported or passive radiator cabinet/enclosure designs.  Even the cabinets can now vary from box to cylinder to spherical!

Front-firing subwoofers employ a speaker mounted so that it radiates the sound from the front or side of the subwoofer cabinet/enclosure.

Down-firing subwoofers employ a speaker that is mounted so that it radiates downward, towards the floor or a base plate.

Porting in some enclosures can also be employed, to force out more air, thus increasing bass response more efficiently than a sealed enclosure.

Hopefully this link will provide more FAQ’s and help: http://www.avforums.com/forums/subwoofers/143350-subwoofer-faqs-guides.html

Enjoy that bass!

Following a number of installations and demo’s where we have had to explain to our customers why a film is taking so long to make it’s appearance, here’s the reason:

The order in which the units in your system e.g. Blu-ray player, AV receiver, TV or Projector are connected is important as to whether or not the HDMI signals will pass through the system. We have found that generally the AV receiver should be turned on first, then the source device(s) e.g. DVD / Blu-ray player or Satellite / Cable and then the Display (TV) / Projector. This all has to do with getting the equipment to ‘handshake’ with each other so the HDCP protection protocol is followed. It is important for anyone programming their universal remote control with single button macros or hot keys to use this sequencing process.  Should this rule of thumb fail, don’t be afraid to swap things around if one unit in the chain is quicker to switch on than another.  Hopefully this helps.